In general, direction control apparatus used in automobile is a device for control direction of it according to driver's intention, and it comprises steering wheel, steering shaft connected to said steering wheel for transmitting operating force, and steering wheel rotation angle sensing device assembled to the steering shaft for sensing steering wheel's rotation angle.
And, vehicle's steering wheel rotation angle sensing device uses magnetic bodies and magnetic sensors for sensing magnetic power of them in said steering wheel's rotation.
Here, conventional magnetic body of vehicle's steering wheel rotation angle sensing device is formed of circular shape and assembled to rotation gear, said magnetic body is not firmly assembled to the rotation gear, so said magnetic body moves freely apart from the rotation gear, and disadvantage of calculation error about rotation angle due to magnetic power variation was occurred.
To solve said problem, conventionally adhesive agent was used in bonding magnetic body to rotation gear.
But, in said bonding method, when the magnetic body rotates in long time, bonding power of said adhesive agent diminishes so that the magnetic body may be detached from the rotation gear, and also bonding process must be added in manufacturing process, it takes more time and manufacturing cost increases in the process.
In the meanwhile, in conventional vehicle's steering wheel rotation angle sensing device when said rotation gear rotates, gear teeth of said rotation gear are in contact state, but gap is occurred between gear tooth of one rotation gear and gear trough of the other rotation gear, so that one rotation gear must rotate more for the gap and power transmission efficiency is lessened by the gap(backlash).
Said backlash is an obstacle for exact rotation angle sensing.